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Dissertation/Thesis Abstract

Chemical Vapor Deposition Growth and Characterization of Monolayer Tungsten Disulfide
by Godin, Kyle André, Ph.D., Stevens Institute of Technology, 2020, 186; 27955263
Abstract (Summary)

Monolayer 2H phase tungsten disulfide (2H-WS2) is a direct gap semiconductor of thickness 0.67 nanometer, a single S-W-S layer of the bulk material. Monolayer WS2 is desired for applications in integrated circuits, photonics, and for electronic devices with novel function based on the spin and valley dependent electronic structure. A key challenge to these applications is controlled growth and contamination-free patterning of large area and high quality samples in both research and industrial scales. This dissertation covers methods and analysis of chemical vapor deposition (CVD) growth of monolayer WS2. Crystal growth is dominated by substrate interactions. The substrate surface energy is engineered to control grain size, nucleation density, preferentially grow monolayer over bulk crystals, and direct patterning. An analysis of the growth mechanism from experimental and thermodynamic considerations is given with a view towards further development of CVD growth processes.

Monolayer WS2 crystals which appear clean under various metrology methods exhibit a wide range of figures of merit for optical and electronic devices, due to varying carrier density and mobility. Photoluminescence was identified as a quick, nondestructive technique that is closer to device figures of merit and can be used to inform growth process development. An analysis of the PL lineshape found that it is sensitive to strain, the substrate, and physisorbed contaminants, which are not the fundamental material quality. Experiments and a discussion of interpreting PL spectra for material quality is given.

Finally, an analysis of atomic force microscopy measurements of monolayer WS2 shows that the true step height is obscured by interactions with surface water, which is different between the material and the substrate. Capiallary forces dominate the tip-sample interactions. A physical description of the source of measurement artifacts and how to correct for contrast inversion is presented.

Indexing (document details)
Advisor: Yang, Eui-Hyeok, Strauf, Stefan
Commitee: Fisher, Frank, Huang, Yuping, Lee, Stephanie, Datta, Dibakar
School: Stevens Institute of Technology
Department: Mechanical Engineer
School Location: United States -- New Jersey
Source: DAI-B 82/1(E), Dissertation Abstracts International
Subjects: Materials science, Nanotechnology
Keywords: 2D materials, Chemical vapor deposition, Tungsten disulfide, WS2
Publication Number: 27955263
ISBN: 9798662408630
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